This invention generally relates to the technical field of metal interconnecting for semiconductor devices. More particularly, it relates to a process for producing a barrier film which is to be located between a copper interconnecting film and an insulation film, a barrier film which is to be located between a film containing Si, GaAs, etc. and a metal interconnecting for preventing silicidation, and a barrier film which is to be located between a highly dielectric film or a ferroelectric film and an electrode.
In recent years, it has been required to more and more speed up the operations of semiconductor devices. To satisfy this requirement, studies have been undertaken on low-resistant copper interconnectings as a substitute for aluminum interconnections.
However, copper occurs as an impurity in semiconductor crystals. In addition, it suffers from a problem of having a large diffusion coefficient in silicon crystals or silicon oxide. Therefore, it has been a practice that a thin film comprising the nitride of a high temperature-melting point metal (a thin tungsten nitride film, etc.) is formed as a barrier film on the surface of a silicon substrate or a thin silicon oxide film and then a copper interconnecting film is formed on the surface of the barrier film.
In order to form such a barrier film, the sputtering method, the heat CVD method or the PE-CVD method is used. In the sputtering method, a high temperature-melting point metal is employed as a target. In the heat CVD method, a thin nitride film is formed by the following reduction reactions. Formula (1) shows a case wherein tungsten is used, while formula (2) shows another case wherein titanium is used.
4WF6+8NH3xe2x86x922W2N+24HF+3N2xe2x80x83xe2x80x83(1)
TiCl4+NH3xe2x86x92TiN+2HCl+1/2H2xe2x80x83xe2x80x83(2)
In case of forming a semiconductor device with multi-layered interconnecting, it is needed to laminate copper interconnections while inserting interlayer insulation films between them. In a semiconductor device to be operated at high speed, the resistance of the copper interconnections as well as the capacity of the interlayer insulation films and the resistance of the barrier films and should be lowered so as to minimize signal transfer delay. More specifically, a barrier film should have a resistance as low as 200 to 300 xcexcxcexa9cm.
Although a thin nitride film having a low resistance can be formed by the sputtering method, only poor step coverage can be achieved thereby. Thus, no uniform barrier film can be formed in a viahole with a high aspect ratio by this method.
In the heat CVD method, on the other hand, a uniform barrier thin film can be formed in a viahole. However, the upper limit of the film-forming temperature in the heat CVD method resides in 400 to 500xc2x0 C., since the dielectric constants of interlayer insulation films with low dielectric constants would be increased when exposed to a high temperature exceeding 500xc2x0 C. At such a low film-forming temperature, the resistivity of, for example, a thin tungsten nitride film attains several thousand xcexcxcexa9cm, which makes it impossible to give barrier films with low resistance.
With respect to the CVD methods, barrier films with low resistance can be formed at a low temperature by the MOCVD method with the use of organometallic compounds or the plasma CVD method. However, the organometallic compounds are expensive, while the plasma CVD method has a problem of achieving only poor step coverage. Thus, these methods are not usable in practice.
The present invention, which has been made to overcome the above-described problems encountered in the conventional art, aims at providing a barrier film having a value of low resistivity and good step coverage.
The present inventors analyzed thin films of high temperature-melting point metal nitrides formed by the conventional heat CVD method and, as a result, found that the high temperature-melting point metal atoms were provided only in an insufficient amount. In the case of tungsten, for example, a tungsten nitride in the conventional art fails to establish the stoichiometric composition (W2N), but shows a composition WxN wherein x ranges from about 1.5 to 1.6. It is assumed that such insufficient supply of metal atoms in a nitride might worsen the crystallinity of the thin nitride film, thereby elevating the value of the resistance.
In the present invention which has been completed based on the above-described finding, attempts are made to approximate the composition of the nitride of a high temperature-melting point metal closely to the stoichiometric level. In order to achieve this object, the present invention relates to a process for producing a barrier film which comprises the steps of providing a substrate in a vacuum atmosphere, introducing a feedstock gas having a high temperature-melting point metal in its structure and a reductive nitrogen-containing gas having a nitrogen atom into said vacuum atmosphere, and forming a thin film of the nitride of said high temperature-melting point metal on said substrate, wherein a nitrogen-free auxiliary reductive gas is introduced into said vacuum atmosphere.
The present invention relates to the process for producing a barrier film, which involves the step of introducing said auxiliary reductive gas together with said feedstock gas and said nitrogen-containing gas into said vacuum atmosphere.
The present invention relates to the process for producing a barrier film, which involves the step of introducing said feedstock gas and said nitrogen-containing gas into said vacuum atmosphere without introducing said auxiliary reductive gas.
The present invention relates to the process for producing a barrier film, wherein, in the step of introducing said auxiliary reductive gas together with said reductive nitrogen-containing gas and said feedstock gas, said reductive nitrogen-containing gas is introduced at a flow rate once or higher than the flow rate of said feedstock gas, and said auxiliary reductive gas is introduced at a flow rate once or more, but not more than 10 times higher than the flow rate of said reductive nitrogen-containing gas.
The present invention relates to the process for producing a barrier film, wherein, in the step of introducing said auxiliary reductive gas together with said reductive nitrogen-containing gas and said feedstock gas, said reductive nitrogen-containing gas is introduced at a flow rate once or more, but not more than 5 times higher than the flow rate of said feedstock gas, and said auxiliary reductive gas is introduced at a flow rate 2 times or more, but not more than 10 times higher than the flow rate of said reductive nitrogen-containing gas.
The present invention relates to the process for producing a barrier film, wherein, in the step of introducing said auxiliary reductive gas together with said reductive nitrogen-containing gas and said feedstock gas, said auxiliary reductive gas is introduced at a flow rate once or more,but not more than 15 times higher than the flow rate of the feedstock gas having said high temperature-melting point metal.
The present invention relates to the process for producing a barrier film, wherein, in the step of growing the thin film of the nitride of said high temperature-melting point metal, a diluent gas not reacting with said high temperature-melting point metal and a gas having an oxygen atom in its chemical structure are introduced so that the pressure of said vacuum atmosphere is regulated to 1 Pa or more, but not more than 100 Pa.
The present invention relates to a process for producing a barrier film which comprises the steps of forming a barrier film made of a thin nitride film of a high temperature-melting point metal on a substrate, wherein the surface of said substrate is exposed to a plasma of hydrogen and a plasma of at least one gas selected from among argon, nitrogen and helium gases, and then the thin film of the nitride of said high temperature-melting point metal is formed on the surface of the substrate.
The invention relates to a barrier film having a thin film of the nitride of a high temperature-melting point metal, wherein said thin nitride film has a content of said high temperature-melting point metal exceeding the stoichiometric composition ratio thereof.
The invention relates to a barrier film having a thin nitride film a high temperature-melting point metal formed on a substrate and aiming at preventing the diffusion of metals in a thin interconnecting film formed on said thin nitride film, wherein said thin nitride film is free from silicon.